What is the Ideal Weight? The Science behind the calculator

The science behind the “Peoples Choice” Ideal Weight formula.

The “Peoples Choice” formula for Ideal Weight was designed by Dr. SB Halls.

Hey, that’s you! You really made this? It’s cool.

Yes, and Thanks!

Its origins and justification are described on this page. The formula tries to predict what other similar people would choose as their own ideal weight.

The Science behind the Ideal Weight Formula

The formula is partly based on the publication by Dr. D. Crawford and K. Campbell1, entitled “Lay definitions of ideal weight and overweight“, from the International Journal of Obesity in 1999. That article published data from an Australian survey which asked people to describe their own perceptions of “ideal weight” and “overweight”.

People were asked: ” Ideally, how much would you like to weigh at the moment?“

The study found that peoples Age and current Weight, correlated with the weight they considered to be ideal. In other words, the heavier people currently are, the heavier they believe their ideal weight is. And older they are, the heavier they set their own ideal weight.

Being devils advocate, are older and heavier people also stupider?

Thanks for asking, in your delicate way.

The opposite is true. It is normal and natural and unavoidable for people to grow heavier as they grow older.

Scientific Study showing the BMI data

The data from the Crawford and Campbell study is shown in the charts below. The authors published their data in units of Body Mass Index ( BMI = kg/m2). Since BMI = weight (in kilograms) divided by height (in meters) squared , their use of BMI allows their data to be applicable to adults with a broad range of height stature.

In the “Age vs Ideal Body Mass Index” chart (above), notice that Men’s mean ideal BMI has less slope than women. Age has little influence on Mens percieved ideal weight, but Age has more influence over how Women perceive their ideal weight.

The second data source for the Peoples Choice Ideal Weight formula, is from the NHANES III study3 which provided a very large dataset of the American population’s height and weights. Correlating the two studies, mens Age does not appear to be an independent variable in how men describe their ideal weight, while mens current BMI strongly influences with their perceived ideal weight. In women, both Age and current weight independently influence their perceived ideal weight.

Halls’ Ideal Body Weight

Using the published data from the Australian study and the more detailed data of Americans from the NHANES III study, Dr. SB Halls created a formula in February 2002, which uses a persons Age, Gender, Height and Current Weight, to predict the mean body weight that a similar average person would say they considered as their “Ideal”. This formula calculates the “Peoples Choice ideal BMI” (in kg/m2), which can then be converted to an ideal body Weight (in kilograms), by multiplying by height (in meters) squared. Weight in kilograms can be converted to pounds by multiplying by 2.2046.

Further Discussion

The publication by Drs Crawford and Campbell1 emphasized the following observations, which are worthy of repeating.

Many men tend to think that their ideal weight is near-to or higher-than a BMI of 25, which is the upper limit of the “medical” non-overweight range. This indicates that men generally under-appreciate the adverse medical risks of being overweight, including diabetes and heart attacks.

The vast majority of women tend to think that their ideal weight is lower than required to be within the non-overweight range.

The heavier that people currently are, the heavier they believe their ideal weight to be. This turns out to be reasonable, because weight from skeletal muscle and bone density also increases with total body weight, up to a certain point.

Are overweight people able to judge their ideal weight as well as non-overweight people? Click here for further discussion of overweight ideal.

Why do Men and Women have different ideas of ideal weight? Click here for further discussion of men and women.

Limitations of the Peoples Choice Ideal Weight Calculator

The PeoplesChoiceIdeal Weight Calculator uses the formulas shown above for Adults, but not for Children. For ages under 18.5 years, the calculator substitutes the 50th percentile weight, according to height, age and gender, determined from NHANES III data. Doing so provides results that have a smooth junction between Adults and Children, for persons of normal weight. This approach is not entirely satisfactory for overweight kids, unfortunately.

This calculator does not have a way to provide reasonable results for people who have extra muscles, such as for bodybuilders or athletes.